1. Field of the Invention
The present invention relates to a process for manufacturing a voltage non-linear resistor comprising zinc oxide as a main ingredient, and to a zinc oxide material which can be suitably used therefor.
2. Related Art Statement
Heretofore, there have been widely known resistors comprising zinc oxide (ZnO) as a main ingredient, and small amounts of additives, such as Bi.sub.2 O.sub.3, Sb.sub.2 O.sub.3, SiO.sub.2, Co.sub.2 O.sub.3, MnO.sub.2 and the like, as an auxiliary ingredient, which exhibit an excellent voltage non-linear characteristic. Utilizing such a characteristic, these resistors have been used in, for example, lightning arresters.
It has been known that in such voltage non-linear resistors mainly comprising zinc oxide, a current impulse withstand capability may be improved by decreasing internal defects of the fired bodies, thus studies of forming and firing conditions have been carried out. Also, an attempt to remove foreign matter has been made by passing slurries through a sieve prior to granulation, as described in Japanese Patent Application Laid-open No. 56-115,503.
However, the above-described conventional processes for decreasing internal defects have presented problems such that satisfactory effects cannot be obtained due to insufficient decrease of the internal defects. This results in a current impulse withstand capability, such as a lightning current impulse withstand capability, switching current impulse withstand capability or the like, that cannot be satisfactorily improved.